1. Field of the Invention
The present invention concerns an imaging tomography apparatus of the type having at least a first acquisition system disposed in a first measurement plane, with a first radiator and a first detector for generation of detector output signals that are a measure of the absorption of the radiation emanating from the first radiator, and a second acquisition system disposed in a second measurement plane, with a second radiator and a second detector for generation of detector output signals that are a measure of the absorption of the radiation emanating from the second radiator, whereby both acquisition systems are mounted to rotate around a common rotation axis. The invention moreover concerns a method for such a tomography apparatus for determination of the relative positions of both acquisition systems.
2. Description of the Prior Art
A tomography apparatus with only one acquisition system is known from German OS 196 15 456 wherein, for correction of image distortions in the reconstructed images, an incorrect angle position between the measurement plane of the acquisition system and the patient table plane is detected.
In contrast to this, German OS 29 16 848 discloses a tomography apparatus with a number of acquisition systems. The acquisition systems are mounted such that they can be adjusted in the direction of the rotational axis so that, depending on the arrangement, alternatively a high scanning speed or scanning of a number of adjacent slices per rotation can be achieved.
A tomography apparatus with a number of acquisition systems is likewise known from German OS 29 51 222, wherein a grid-controlled x-ray tube that is contained in a separate housing together with the filament transformer is used as the x-ray radiator for fast activation and deactivation of an x-ray beam.
Other tomography apparatuses with at least two acquisition systems are known, for example, from U.S. Pat. Nos. 4,991,190 and 6,421,412. The advantage of such tomography apparatuses with a number of acquisition systems compared to an apparatus with a single acquisition system is the capability to examine a subject with an increased sampling speed or with an increased sampling resolution. A high sampling speed is of importance when movement artifacts that are caused by voluntary or involuntary movements of the subject (for example of an organ of an organism to be examined) must be minimized in the reconstructed image. In the examination (for example of a heart), for reconstruction of an artifact-free slice or volume image it is necessary that all exposures used for the reconstruction optimally record the same movement state (phase) of the heart at the various rotation angle positions.
In addition to single image acquisition, entire sequences of slice or volume images are generated for representation of movement cycles for medical examinations. A higher sampling speed thereby offers the advantage of an improved temporal resolution of the imaged region affected by a movement cycle so that rapidly-changing movement states can be acquired.
A tomography apparatus with a number of acquisition systems also can be operated such that a higher sampling resolution is achieved compared to a tomography apparatus with only one acquisition system. This is particularly of importance when organs or organ parts of an organism must be resolved in a small examination volume, as is the case, for example, for an examination of blood vessels.
In a tomography apparatus with a number of acquisition systems, the acquired detector output signals of the various acquisition systems are combined with one another for reconstruction of a slice or volume image, both in the operating mode to increase the sampling speed and in the operating mode to increase the sampling resolution. The reconstruction of a slice or volume image from data of various acquisition systems thereby always ensues based on the prior knowledge of the position of the first measurement plane relative to the position of the second measurement plane.